1. Field of the Invention:
This invention relates to the production of metal/refractory composites. In particular, the invention relates to the production of composites of metals or alloys reinforced with discontinuous refractory particles formed by bubbling a reactive gas through a melt.
2. Background of the Invention
In recent decades, metal matrix composites have been developed with properties superior to those of traditional materials. Since the late 1980""s, lightweight alloy matrix composites have been developed for many applications. In particular, discontinuously reinforced lightweight alloy matrix composites are rapidly emerging as new low cost alternatives to continuously reinforced composites for automobile and aerospace applications.
These discontinuously reinforced alloy composites are commercially produced by incorporating advanced ceramic particles into the molten alloy. High costs associated with industrial production of the advanced ceramic particles using an electric resistance furnace raise the costs associated with the composites.
Various attempts at in-situ formation of ceramic particles in an alloy matrix have been reported. For example, U.S. Pat. No. 5,626,692 discloses a method of making an aluminum-based metal matrix composite where a carbide reinforcement is produced from a solid carbon source. U.S. Pat. No. 4,808,372 discloses an in-situ process for producing a composite containing a refractory material dispersed in a solid matrix. However, the low production rates, complex methods of operation and high costs associated with these in-situ processes are not satisfactory.
The present invention provides a method of making a metal/refractory composite in which the composite metal matrix is reinforced with discontinuous refractory particles. According to the invention, a gas including at least one gaseous refractory forming component is bubbled through a melt including a metal matrix forming component and at least one molten refractory forming component. The bubbled gas forms a foam on top of the melt. Reaction of the gaseous refractory forming component and the molten refractory forming component forms refractory particles in the melt and in the foam. The refractory particles are enriched in the foam relative to the melt. When the foam breaks, a slurry containing the refractory particles is formed that can be cast in molds. Upon cooling, a solid metal/refractory composite is formed in which a metal or alloy is discontinuously reinforced with the refractory particles.
A continuous method of forming metal/refractory composites is provided by introducing the melt and gas to a melt container while removing the foam produced. High production rates with excellent compositional control are possible in a simple, easily controlled process using inexpensive raw materials.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.